Micro-strip transmission line structure of a serpentine type

ABSTRACT

A micro-strip transmission line capable of reducing far-end crosstalk is provided. The micro-strip transmission line having a serpentine shape is capable of reducing the far-end crosstalk of the transmission line by increasing capacitive coupling between neighboring transmission lines by allowing parallel micro-strip transmission lines to have serpentine shapes. In the structure of the micro-strip transmission line having the serpentine shape, it is possible to reduce the far-end crosstalk of the transmission line by increasing capacitive coupling between neighboring transmission lines by allowing parallel micro-strip transmission lines to have serpentine shapes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a micro-strip transmission line capableof reducing far-end crosstalk, and more particularly, to a structure ofa micro-strip transmission line having a serpentine shape for reducingfar-end crosstalk of a transmission line by increasing capacitivecoupling between neighboring transmission lines by allowing parallelmicro-strip transmission lines to have serpentine shapes.

2. Description of the Related Art

Crosstalk is caused by electromagnetic interference between neighboringsignal lines. When a high frequency signal is transmitted through twoparallel long signal lines, signals transmitted through one or twosignal lines mutually interfere with one another. A transmission loss isincreased due to the crosstalk caused by the mutual interference.

Capacitive coupling caused by mutual capacitance and inductive couplingcaused by mutual inductance occur between the two signal lines. Far-endcrosstalk is caused by a difference between the capacitive couplingcaused by the mutual capacitance and the inductive coupling caused bythe mutual inductance.

FIG. 1 illustrates a structure of a conventional micro-striptransmission line.

In FIG. 1, two parallel micro-strip transmission lines are shown. An endof each transmission line is terminated with a resistor havingresistance the same as the characteristic impedance of the transmissionline.

A transmission line through which a signal is applied to an end (asending end) thereof between two transmission lines is referred to as anaggressor line 10. The other transmission line through which a signal isnot applied is referred to as a victim line 20. Far-end crosstalkV_(FEXT) of the victim line 20 may be represented by Equation 1 asfollows:

$\begin{matrix}{{{V_{FEXT}(t)} = {\frac{TD}{2} \cdot ( {\frac{C_{m}}{C_{T}} - \frac{L_{m}}{L_{S}}} ) \cdot \frac{\partial{V_{a}( {t - {TD}} )}}{\partial t}}},} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$

where, TD is a transmission time taken to transmit a signal through atransmission line, C_(m) is mutual capacitance per unit length, C_(T) isa sum of self capacitance per unit length and the mutual capacitance,L_(m) is mutual inductance per unit length, and L_(S) is self inductanceper unit length. Here, V_(a)(t) is a voltage applied to a sending-end ofthe aggressor line.

In case of a transmission line located in a homogeneous medium such as astrip line, a capacitive coupling amount is the same as an inductivecoupling amount. Ideally, the far-end crosstalk becomes zero.

However, in case of a micro-strip line formed on a printed circuit board(PCB), the inductive coupling amount is greater than the capacitivecoupling amount. Thus, the far-end crosstalk has a negative value.Although the strip-line transmission line can remove the far-endcrosstalk, the strip-line transmission line has to use more layers ofthe PCB than the micro-strip line. Accordingly, costs are increased.

When independent signals are respectively applied to two parallelmicro-strip lines, a case where two applied signals are changed to thesame direction is referred to as an even mode, and a case where the twoapplied signals are changed to different directions is referred to anodd mode.

FIG. 2 illustrates concepts of even and odd modes.

Referring to FIG. 2, if an applied signal is increased with respect totime, far-end crosstalk has a negative pulse shape. Accordingly, thefar-end crosstalk delays a signal change with respect to time in theeven mode. On the contrary, the far-end crosstalk advances a signalchange with respect to time in the odd mode.

That is, in the even mode, a signal transmission time is slightlyincreased. In the odd mode, the signal transmission time is slightlydecreased. A difference in the signal transmission time between the evenand odd modes is represented by Equation 2 as follows:

$\begin{matrix}{{{TD}_{EVEN} - {TD}_{ODD}} = {l \cdot \sqrt{L_{S}C_{T}} \cdot ( {\frac{L_{m}}{L_{S}} - \frac{C_{m}}{C_{T}}} )}} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack\end{matrix}$

where, l is a length of a transmission line, TD_(EVEN) is a transmissiontime in an even mode, TD_(ODD) is a transmission time in an odd mode,C_(m) is mutual capacitance per unit length, C_(T) is a sum of selfcapacitance per unit length and the mutual capacitance, L_(m) is mutualinductance per unit length, and L_(S) is self inductance per unitlength.

FIG. 3 illustrates influences of crosstalk in even and odd modes.

Referring to FIG. 3, in a case where random data signals are applied tosending ends of two parallel micro-strip transmission lines, timingjitter due to a difference in rise-time at a receiving-end between evenand odd modes which is caused by a difference in arriving time ofsignals between the even and odd modes occurs.

In methods of reducing the crosstalk effect occurring at the micro-striptransmission line, a spacing between signal lines is increased, or aguard trace is used. The guard trace is a structure for reducingcoupling between neighboring signal lines by inserting a parallel tracebetween the signal lines. However, in the aforementioned methods, themicro-strip transmission lines occupy too large area in the PCB.

SUMMARY OF THE INVENTION

The present invention provides a structure of a micro-strip transmissionline having a serpentine shape capable of reducing far-end crosstalk ofa transmission line by increasing capacitive coupling betweenneighboring transmission lines by allowing parallel micro-striptransmission lines to have serpentine shapes.

According to an aspect of the present invention, there is provided astructure of a micro-strip transmission line having a serpentine shape,comprising: a first micro-strip transmission line; and a secondmicro-strip transmission line spaced apart from and parallel with thefirst micro-strip transmission line, wherein the first and secondmicro-strip transmission lines include at least one unit serpentinestructure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a structure of a conventional micro-striptransmission line.

FIG. 2 illustrates concepts of even and odd modes.

FIG. 3 illustrates influences of crosstalk noise in even and odd modes.

FIG. 4 illustrates a unit serpentine structure of a structure of amicro-strip transmission line having a serpentine shape according to anembodiment of the present invention.

FIG. 5 illustrates a structure of a micro-strip transmission line havinga serpentine shape which includes two micro-strip transmission linesaccording to an embodiment of the present invention.

FIG. 6 illustrates a structure of a micro-strip transmission line havinga serpentine shape which includes three or more micro-strip transmissionlines according to another embodiment of the present invention.

FIG. 7 illustrates a difference between a capacitive coupling ratio KCand an inductive coupling ratio KL based on a length D of a unitserpentine structure.

FIG. 8 illustrates a change of a waveform of a crosstalk voltage in acase where a length D of a unit serpentine structure is changed.

FIG. 9 is an eye-diagram of a micro transmission line according to aconventional technique.

FIG. 10 is an eye-diagram of a structure of a micro-strip transmissionline having a serpentine shape according to an embodiment of the presentinvention.

FIG. 11 illustrates timing jitter caused by a difference in transmissiontime between even and odd modes.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described in detail byexplaining exemplary embodiments of the invention with reference to theattached drawings.

FIG. 4 illustrates a unit serpentine structure of a structure of amicro-strip transmission line having a serpentine shape according to anembodiment of the present invention.

As shown in FIG. 4, a serpentine structure 400 according to theembodiment of the present invention includes a first verticalmicro-strip transmission line 410, a first horizontal micro-striptransmission line 420, a second vertical micro-strip transmission line430, and a second micro-strip transmission line 440.

Unlike a structure of conventional micro-strip transmission lines thatare parallel straight lines, if a serpentine structure is used, mutualcapacitance between neighboring signal lines is increased. In theserpentine structure, since a component perpendicular to a lengthdirection of a micro-strip transmission line is perpendicular to adirection in which current proceeds, the mutual capacitance isincreased, but the mutual inductance is not considerably increased.

Accordingly, as shown in FIG. 4, in the micro-strip transmission lineincluding unit serpentine structures, the mutual inductance is notconsiderably increased, but the mutual capacitance is largely increased.Thus, far-end crosstalk and timing jitter caused by crosstalk arereduced.

At this time, as a length D of the unit serpentine structure isdecreased, that is, as a serpentine degree is increased, the capacitivecoupling is increased. However, in a case where the length D of the unitserpentine structure is too small, that is, the transmission lines tooserpentine, the capacitive coupling becomes greater than the inductivecoupling.

FIG. 5 illustrates a structure of a micro-strip transmission line havinga serpentine shape which includes two micro-strip transmission linesaccording to an embodiment of the present invention.

As shown in FIG. 5, the structure of the micro-strip transmission linehaving the serpentine shape according to the embodiment of the presentinvention includes a first micro-strip transmission line 401 and asecond micro-strip transmission line 402 that is spaced apart from andparallel with the first micro-strip transmission line 401.

At this time, the first and second micro-strip transmission lines 401and 402 include a plurality of unit serpentine structures.

The unit serpentine structure is constructed with a first verticalmicro-strip transmission line 411, 412, a first horizontal micro-striptransmission line 421, 422, a second vertical micro-strip transmissionline 431, 432, and a second horizontal micro-strip transmission line441, 442.

The first vertical micro-strip transmission line 411, 412 isperpendicular to length directions of the first and second micro-striptransmission lines 401 and 402. The first vertical micro-striptransmission line 411, 412 has a predetermined length S2, apredetermined width W2, and a rectangular cross section.

The first horizontal micro-strip transmission line 421, 422 has aterminal connected to a side of the first vertical micro-striptransmission line 411, 412 in a length direction of the first verticalmicro-strip transmission line 411, 412. The first horizontal micro-striptransmission line 421, 422 is parallel with the length direction of thefirst and second micro-strip transmission lines 401 and 402. Inaddition, the first horizontal micro-strip transmission line 421, 422have a predetermined length, a predetermined width W1, and a rectangularcross section.

The second vertical micro strip transmission line 431, 432 have aterminal connected to a terminal of the first horizontal micro-striptransmission line 421, 422 in a length direction of the second verticalmicro strip transmission line 431, 432. The second vertical micro striptransmission line 431, 432 is perpendicular to the length direction ofthe first and second micro-strip transmission line 401 and 402. Inaddition, the second vertical micro-strip transmission line 431, 432 hasa predetermined length, a predetermined width W2, and a rectangularcross section.

The second horizontal micro strip transmission line 441, 442 has aterminal connected to the other side of the second vertical micro-striptransmission line 431, 432 in a length direction of the second verticalmicro-strip transmission line 431, 432. The second horizontal microstrip transmission line 441, 442 is parallel with the length directionof the first and second micro-strip transmission line 401 and 402. Inaddition, the second horizontal micro-strip transmission line 441, 442has a predetermined length, a predetermined width W1, and a rectangularcross section.

In addition, the first vertical micro-strip transmission line 411, 412,the first horizontal micro-strip transmission line 421, 422, the secondvertical micro-strip transmission line 431, 432, and the secondhorizontal micro-strip transmission line 441, 442 are successivelyarranged.

The first horizontal micro-strip transmission line 421 in the firstmicro-strip transmission line 401 is disposed nearest to the secondmicro-strip transmission line 402. The second horizontal micro-striptransmission line 441 in the first micro-strip transmission line 401 isdisposed farthest from the second micro-strip transmission line 402.

On the other hand, the first horizontal micro-strip transmission line422 in the second micro-strip transmission line 402 is disposed farthestfrom the first micro-strip transmission line 401. The second horizontalmicro-strip transmission line 422 in the second micro-strip transmissionline 402 is disposed nearest to the first micro-strip transmission line401.

At this time, the first and second horizontal micro-strip transmissionlines 421, 422 and 441, 442 have the same width W1. The first and secondvertical micro-strip transmission lines 411, 412 and 431, 432 have thesame width W2.

On the other hand, the first and second vertical micro-striptransmission lines 411, 412 and 431, 432 have the same length.

The first and second vertical micro-strip transmission lines 412 and 432in the second micro-strip transmission line 402 are disposed at the samepositions as the first and second vertical micro-strip transmissionlines 411 and 431 in the first micro-strip transmission line 401 ordisposed within the width W2 of the first vertical micro-striptransmission line 411 from the first and second vertical micro-striptransmission lines 411 and 431, in the length direction of the secondmicro-strip transmission line 402.

The second horizontal micro-strip transmission line 442 in the secondmicro-strip transmission line 402 is disposed at the same position asthe second horizontal micro-strip transmission line 441 in the firstmicro-strip transmission line 401 or disposed within the width W2 of thefirst vertical micro-strip transmission line 411, in the lengthdirection of the second micro-strip transmission line 402.

The width W2 of the first and second vertical micro-strip transmissionlines 411 and 431 (412 and 432) may range from 0.1 to 5 times of thewidth W1 of the first and second horizontal micro-strip transmissionlines 421, 422 and 441, 442.

The length S2 of the first and second vertical micro-strip transmissionlines 411, 412 and 431, 432 may range from one to seven times of thewidth W1 of the first and second horizontal micro-strip transmissionlines 421, 422 and 441, 442.

A spacing S1 between the first vertical micro-strip transmission line411 in the first micro-strip transmission line 401 and the firstvertical micro-strip transmission line 412 in the second micro-striptransmission line 402 may range from 0.0001 to 5 times of the width W1of the first and second horizontal micro-strip transmission lines 421and 441 (422 and 442).

In the structure of the micro-strip transmission line having theserpentine shape according to the embodiment of the present invention,it is possible to reduce cross talk at a receiving-end by reducing adifference between mutual capacitance and mutual inductance by adjustinga length D of the first micro-strip transmission line in the unitserpentine structure in the length direction of the first micro-striptransmission line.

FIG. 6 illustrates a structure of a micro-strip transmission line havinga serpentine shape which includes three or more micro-strip transmissionlines according to another embodiment of the present invention.

As shown in FIG. 6, the structure of the micro-strip transmission linehaving the serpentine shape according to the embodiment of the presentinvention may be constructed with three or more micro-strip transmissionlines 401 to 403.

FIG. 7 illustrates a difference between a capacitive coupling ratio(KC=C_(m)/C_(T)) and an inductive coupling ratio (KL=L_(m)/L_(S)) basedon a length D of a unit serpentine structure.

A graph of FIG. 7 is obtained by calculating a difference betweencapacitive coupling and inductive coupling by using L_(S), L_(m), C_(T),and C_(m) obtained through a field solver simulation. Here, HFSS of theAnsoft Company is used as the field solver.

Widths W1 and W2 of the first and second micro-strip transmission linesare 14 mils. A spacing between the first and second micro-striptransmission lines is 19 mils. It is assumed that a printed circuitboard (PCB) has two layers and that thicknesses of dielectric and coppermembers are 8 mils and 0.7 mils, respectively.

As the length D of the unit serpentine structure decreases, thecapacitive coupling increases. In a case where the length D of the unitserpentine structure is 80 mils, the capacitive coupling isapproximately the same as the inductive coupling. In a case where thelength D of the unit serpentine structure is less than 80 mils, thecapacitive coupling becomes greater than the inductive coupling.

FIG. 8 illustrates a change of a waveform of a far-end crosstalkvoltage, when a length D of a unit serpentine structure is changed.

A graph of FIG. 8 is obtained by performing a SPICE simulation by usingL_(S), L_(m), C_(T), and C_(m) obtained by using the field solver.

A length of the first and second micro-strip transmission lines is 8inch. Both ends of all the transmission lines are terminated by usingtermination resistors of 50Ω that is the same as the characteristicimpedance of the transmission lines. A voltage of 0.4 V having arise-time of 50 ps is applied to the first micro-strip transmission line(aggressor line). A voltage waveform of far-end crosstalk is measured atan end of the second micro-strip transmission line (victim line). Thefar-end crosstalk voltage is reduced as compared with the conventionaltechnique.

Specifically, in a case where the length D of the unit serpentinestructure is 80 mils, the far-end crosstalk is substantially removed.However, in a case where the length D of the unit serpentine structureis 56 mils by allowing the micro-strip transmission lines to serpentinetoo much, the capacitive coupling becomes greater than the inductivecoupling. Positive far-end crosstalk occurs.

FIG. 9 is an eye-diagram of a micro transmission line according to aconventional technique. FIG. 10 is an eye-diagram of a structure of amicro-strip transmission line having a serpentine shape according to anembodiment of the present invention.

In FIG. 10, timing jitter caused by a difference in transmission timebetween even and odd modes is obtained through the SPICE simulation withrespect to the structure of the micro-strip transmission line having theserpentine shape.

A 27-1 pseudo random binary sequence (PRBS) pattern and a 215-1 PRBSpattern are applied to sending ends of first and second micro-striptransmission lines (aggressor and victim lines), respectively. Awaveform is measured at a receiving end of the second micro-striptransmission line (victim line). Timing jitter in an eye diagram of thestructure of the micro-strip transmission line having the serpentineshape according to the embodiment of the present invention considerablydecreases to 5.88 ps as compared with 49.6 ps in the conventionaltechnique.

FIG. 11 illustrates a timing jitter due to difference in transmissiontime between even and odd modes.

Referring to FIG. 11, in the present invention, timing jitter isconsiderably reduced as compared with the conventional technique. Likethe voltage waveform of far-end crosstalk, in a case where a length D ofa unit serpentine structure is 80 mils, the timing jitter is minimized.In a case where the length D of the unit serpentine structure becomesless than 80 mils, the timing jitter is increased. This is because thecapacitive coupling is increased too much to become greater than theinductive coupling.

In a structure of a micro-strip transmission line having the serpentineshape according to an embodiment of the present invention, it ispossible to reduce far-end crosstalk of the transmission lines byincreasing capacitive coupling between neighboring transmission lines byallowing parallel micro-strip transmission lines to have serpentineshapes.

In addition, it is possible to reduce an area of a printed circuit board(PCB) and costs by efficiently reducing far-end crosstalk withoutincreasing a spacing between two signals lines and without a guardtrace.

In addition, it is possible to increase a signal transmission speed byreducing timing jitter caused by a difference in transmission timebetween even and odd modes by increasing only mutual capacitance withoutchanging mutual inductance in the structure of the micro-striptransmission line having the serpentine shape according to an embodimentof the present invention.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of thepresent invention as defined by the appended claims.

1. A structure of a micro-strip transmission line having a serpentineshape, comprising: a first micro-strip transmission line; and a secondmicro-strip transmission line spaced apart from and parallel with thefirst micro-strip transmission line, wherein the first and secondmicro-strip transmission lines include at least one unit serpentinestructure, and wherein the unit serpentine structure includes: a firstvertical micro strip transmission line perpendicular to a lengthdirection of the first and second micro-strip transmission lines; afirst horizontal micro-strip transmission line including a terminalconnected to a side of the first vertical micro-strip transmission linein a length direction of the first vertical micro-strip transmissionline, the first horizontal micro-strip transmission line being parallelwith the length direction of the first and second micro-striptransmission line; a second vertical micro-strip transmission lineincluding a side connected to the other terminal of the first horizontalmicro-strip transmission line in a length direction of the secondvertical micro-strip transmission line, the second vertical micro-striptransmission line being perpendicular to the length direction of thefirst and second micro-strip transmission line; and a second horizontalmicro-strip transmission line including a terminal connected to theother side of the second vertical micro-strip transmission line in thelength direction of the second vertical micro-strip transmission line,the second horizontal micro-strip transmission line being parallel withthe length direction of the first and second micro-strip transmissionline, wherein the first vertical micro-strip transmission line, thefirst horizontal micro-strip transmission line, the second verticalmicro-strip transmission line, and the second horizontal micro-striptransmission line are successively arranged.
 2. (canceled)
 3. Thestructure of the micro-strip transmission line of claim 2, wherein thefirst horizontal micro-strip transmission line in the first micro-striptransmission line is disposed nearest to the second micro-striptransmission line, and wherein the second horizontal micro-striptransmission line in the first micro-strip transmission line is disposedfarthest from the second micro-strip transmission line.
 4. The structureof the micro-strip transmission line of claim 2, wherein the firsthorizontal micro-strip transmission line in the second micro-striptransmission line is disposed farthest from the first micro-striptransmission line, and wherein the second horizontal micro-striptransmission line in the second micro-strip transmission line isdisposed nearest to the first micro-strip transmission line.
 5. Thestructure of the micro-strip transmission line of claim 4, wherein thefirst and second horizontal micro-strip transmission lines have the samewidth.
 6. The structure of the micro-strip transmission line of claim 5,wherein the first and second vertical micro-strip transmission lineshave the same width.
 7. The structure of the micro-strip transmissionline of claim 6, wherein the first and second vertical micro-striptransmission lines have the same length.
 8. The structure of themicro-strip transmission line of claim 7, wherein the first and secondvertical micro-strip transmission lines in the second micro-striptransmission line are disposed at the same positions as the first andsecond vertical micro-strip transmission lines in the first micro-striptransmission line or disposed within the width of the first verticalmicro-strip transmission line from the first and second verticalmicro-strip transmission lines, in the length direction of the secondmicro-strip transmission line.
 9. The structure of the micro-striptransmission line of claim 7, wherein the second horizontal micro-striptransmission line in the second micro-strip transmission line isdisposed at the same position as the second horizontal micro-striptransmission line in the first micro-strip transmission line or disposedwithin the width of the first vertical micro-strip transmission line, inthe length direction of the second micro-strip transmission line. 10.The structure of the micro-strip transmission line of claim 7, whereinthe width of the first and second vertical micro-strip transmissionlines may range from 0.1 to 5 times of the width of the first and secondhorizontal micro-strip transmission lines.
 11. The structure of themicro-strip transmission line of claim 7, wherein the length of thefirst and second vertical micro-strip transmission lines may range fromone to seven times of the width of the first and second horizontalmicro-strip transmission lines.
 12. The structure of the micro-striptransmission line of claim 7, wherein a spacing between the firstvertical micro-strip transmission line in the first micro-striptransmission line and the first vertical micro-strip transmission linein the second micro-strip transmission line may range from 0.0001 to 5times of the width of the first and second horizontal micro-striptransmission lines.
 13. The structure of the micro-strip transmissionline of claim 7, wherein a difference between mutual capacitance andmutual inductance is reduced by adjusting a length D of the unitserpentine structure in the length direction of the first micro-striptransmission line.
 14. The structure of the micro-strip transmissionline of claim 2, further comprising at least one third micro-striptransmission line including at least one unit serpentine structure whichis spaced apart from and parallel with the first and second micro-striptransmission lines.